Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $207.76   8.255%   $224.9106   $224.91   $224.90   $224.90  
  Purchase #2 $243.82   9.554%   $267.1146   $267.11   $267.10   $267.10  
  Purchase #3 $58.60   6.189%   $62.2268   $62.23   $62.25   $62.20  
  Purchase #4 $17.71   7.585%   $19.0533   $19.05   $19.05   $19.10  
  Purchase #5 $231.95   4.733%   $242.9282   $242.93   $242.95   $242.90  
  Purchase #6 $153.70   7.262%   $164.8617   $164.86   $164.85   $164.90  
  Purchase #7 $139.39   12.489%   $156.7984   $156.80   $156.80   $156.80  
  7 purchase totals = $1,052.93       $1,137.8936   $1,137.89   $1,137.90   $1,137.90